exhaustive field / variant は今では #[non_exhaustive] が使えるわね
rfcs/2008-non-exhaustive.md at master · rust-lang/rfcs
https://github.com/rust-lang/rfcs/blob/master/text/2008-non-exhaustive.md
rust/RELEASES.md at 1.41.1 · rust-lang/rust
https://github.com/rust-lang/rust/blob/1.41.1/RELEASES.md#language-1
Rust 1.40 からです